The treatment of waste, whether generated through municipal collection systems or through a broad range of industries, may be observed to vary from simple land-fill techniques to somewhat sophisticated pyrogenic, chemical or biochemical conversion methods. With the latter, chemical approach, significant capital commitments generally are called for which require justification by virtue of the degree of environmental protection achieved and/or the generation of monetarily profitable products and by-products of waste.
Controlled composing procedures are considered to offer significant promise in the treatment of biodegradable industrial and municipal wastes and the compost product generated thereby represents a valuable and readily saleable product. A desired approach to treatment of wastes by biodegradation is one wherein composting is carried out in the thermophilic phase at temperatures of about 45.degree.-50.degree. C. At such temperatures, bacteria otherwise active in the mesophilic phase at lower temperatures are avoided and noxious odors are not evolved in the course of digestion.
To achieve a marketable compost product, a waste treatment process should be carried out wherein raw refuse is passed through a variety of screening, shredding and separation stages. These stages serve to remove inorganic components such as metals and plastics and effect a reduction of average waste particle size suitable to permit the derivation of a uniform moisture content throughout the organic material. The thus-treated raw waste represents the starting material for a composting process which, to achieve a marketable end compost product, must during digestion substantially provide a continuous uniformity of material and moisture, proper mixing and aeration as digestive breakdown occurs.
One important and highly practical approach to carrying out thermophilic digestion is that of windrowing the waste material. With this approach, long rows of waste are developed which are laterally transferred across the surface of a treatment region and, in consequence of this manipulation, are aerated and agitated. Thus, the waste material progressively is transferred from one row position to a next, for example, from right to left, across the treatment region over a period of time until a last row position is reached at which point the digestive process is completed. The resultant fully digested compost represents a most valuable soil additive.
More advanced windrowing facilities, described, for example, in U.S. Pat. No. 4,302,236, by Roman, assigned in common herewith, provide a somewhat expansive graded and paved surface for windrow development. In addition to providing for moisture input to the composting material, these treatment surfaces are designed for environmental protection and for enhancing the aeration of composting waste by providing controlled blown air inputs beneath each elongate windrow. Thus, with this more advanced windrowing technique, a long windrow of waste having been treated by separation of certain inorganic materials and shredding is initially deposited along a first row position and, if necessary, adjustment of moisture content is made. Row positioning is such that the material is deposited over a first elongate air duct to provide for the blowing of air upwardly thereinto. As thermophilic decomposition ensues, a windrowing machine must be employed to agitate, mix and move the windrow material to a position over a next parallel succeeding air duct to continue the process. This movement of the windrow piles is highly important, providing necessary intermixing of thermophilic bacteria with the material and permitting air access thereinto. During periods of rainfall, individual windrows being treated may receive an excess of moisture and for such conditions, the windrow machines should be capable of agitating and mixing the material without transferring it from one row position to the next. Digestion of the material within the windrows also is affected by the size of the windrow piles in terms of their height, as well as by the symmetry of the piles which are developed. Particularly where air is forced through the piles from elongate ducts located at the bottom thereof, improved aeration is achieved with the development of symmetrical windrow cross-section.
A variety of windrowing machines have been proposed or employed by the industry. One such machine currently utilized incorporates an elevating device which resembles a flight conveyor having a series of parallel, elongate paddles which are mutually interconnected by continuous chains and driven by a hydraulic motor. In operation, a rather large front end loader is utilized to suspend the elevator or conveyor at an angle both with respect to the ground and the axis of the windrow pile while moving forward at a relatively low speed, for instance 1 m.p.h., such that the lower disposed region or side of the elevator confronts the row of material and, in effect, thrusts it into an adjacent row. The type of front end loader employed for this procedure necessarily is rather large, typically, a 202 hp loader weighing about 2,600 tons being required.
In U.S. Pat. No. 4,290,703, entitled "Windrowing-Type Composting Apparatus", by Roman, and assigned in common herewith, apparatus is provided wherein a flight-type windrow elevator or conveyor is supported forwardly upon a rigid frame which, in turn, is supported by three freely rotatable wheels. By so positioning these wheels about the frame, the windrow conveyor is properly positioned to confront a row of waste material being transferred and the supporting wheels of the frame of the apparatus do not encounter the waste. This device is configured for connection with a front-end loader and may utilize a self-contained motor for providing hydraulic power to the wndrow conveyor components. Lower powered front-end loaders or the like may be utilized with this improved apparatus. A frame mounted conveyor of similar configuration which is self-propelled is disclosed in U.S. application for patent, Ser. No. 255,752, entitled "Windrowing Type Composting Apparatus", by Roman, filed Apr. 20, 1981, and assigned in common herewith.
The type windrowing apparatus described above, while effective for typical utilization, has limitations with respect to the size of windrow pile which can be developed. Additionally, such windrowing devices necessarily develop nonsymmetrical windrow cross sections. Further, it is necessary to provide right-hand and left-hand sense devices for any given installation to avoid a gradual material creep along the longitudinal axis of the windrow piles in the course of shifting them from one position to the next. Of course, such devices are not practical for use in agitating windrowed material without moving the windrow laterally.